Providing indirect data addressing for a control block at a channel subsystem of an i/o processing system

ABSTRACT

An computer program product, apparatus, and method for facilitating input/output (I/O) processing for an I/O operation at a host computer system configured for communication with a control unit. The computer program product includes a tangible storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method. The method includes the host computer system obtaining a transport command word (TCW) for an I/O operation. The TCW specifies a location of one or more I/O commands and a flag set to indicate that the location is an indirect address. The host computer system extracts the location of the one or more I/O commands and the flag from the TCW, gathers the one or more I/O commands responsive to the location specified by the TCW and the flag, and then forwards the one or more I/O commands to the control unit for execution.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 12/031,201, filed Feb. 14, 2008, entitled “PROVIDING INDIRECTDATA ADDRESSING FOR A CONTROL BLOCK AT A CHANNEL SUBSYSTEM OF AN I/OPROCESSING SYSTEM”, by Flanagan et al., which is hereby incorporatedherein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present disclosure relates generally to input/output (I/O)processing, and in particular, to providing indirect data addressing fora control block at a channel subsystem of an I/O processing system.

2. Description of Background

Input/output (I/O) operations are used to transfer data between memoryand I/O devices of an I/O processing system. Specifically, data iswritten from memory to one or more I/O devices, and data is read fromone or more I/O devices to memory by executing I/O operations.

To facilitate processing of I/O operations, an I/O subsystem of the I/Oprocessing system is employed. The I/O subsystem is coupled to mainmemory and the I/O devices of the I/O processing system and directs theflow of information between memory and the I/O devices. One example ofan I/O subsystem is a channel subsystem. The channel subsystem useschannel paths as communications media. Each channel path includes achannel coupled to a control unit, the control unit being furthercoupled to one or more I/O devices.

The channel subsystem may employ channel command words (CCWs) totransfer data between the I/O devices and memory. A CCW specifies theI/O command to be executed. For commands initiating certain I/Ooperations, the CCW designates the memory area associated with theoperation, the action to be taken whenever a transfer to or from thearea is completed, and other options.

During I/O processing, a list of CCWs is fetched from memory by achannel. The channel parses each command from the list of CCWs andforwards a number of the commands, each command in its own entity, to acontrol unit coupled to the channel. The control unit then processes thecommands. The channel tracks the state of each command and controls whenthe next set of commands are to be sent to the control unit forprocessing. The channel ensures that each command is sent to the controlunit in its own entity. Further, the channel infers certain informationassociated with processing the response from the control unit for eachcommand.

Performing I/O processing on a per CCW basis may involve a large amountof processing overhead for the channel subsystem, as the channels parseCCWs, track state information, and react to responses from the controlunits. Therefore, it may be beneficial to shift much of the processingburden associated with interpreting and managing CCW and stateinformation from the channel subsystem to the control units. Simplifyingthe role of channels in communicating between the control units and anoperating system in the I/O processing system may increase communicationthroughput as less handshaking is performed. Simplifying the role ofchannels in communication may include grouping multiple commands into asingle I/O operation. Altering command sequences by grouping two or morecommands together in a single I/O operation results in a larger dataarea required for storing the commands and a data area whose lengthvaries depending on the size and number of commands that are groupedwithin the single I/O operation.

Currently, a single I/O operation can support a single fixed sizedcommand data area that is referenced by a single direct address. Thislimits the number of commands that can be grouped together in a singleI/O operation and thus, limits the increase in throughput that can begained by grouping commands. In addition, this limits the way that thecommands are stored to a contiguous storage area. Performance may beimproved by having the commands spread out in a variety of locations.Accordingly, there is a need in the art to be able to store a pluralityof commands making up a single I/O operation in non-contiguous storageand for the amount of storage required to be able to vary betweendifferent I/O operations.

BRIEF SUMMARY OF THE INVENTION

An exemplary embodiment includes a computer program product forfacilitating input/output (I/O) processing for an I/O operation at ahost computer system configured for communication with a control unit.The computer program product includes a tangible storage medium readableby a processing circuit and storing instructions for execution by theprocessing circuit for performing a method. The method includes the hostcomputer system obtaining a transport command word (TCW) for an I/Ooperation. The TCW specifies a location of one or more I/O commands anda flag. The flag is set to indicate that the location is an indirectaddress. The host computer system extracts the location of the one ormore I/O commands and the flag from the TCW. The host computer systemgathers the one or more I/O commands responsive to the locationspecified by the TCW and the flag, and then forwards the one or more I/Ocommands to the control unit for execution.

Another exemplary embodiment includes an apparatus for providingindirect data addressing for a control block at a host computer systemconfigured for communication with a control unit. The host computersystem obtains a TCW for an I/O operation. The TCW specifies a locationof one or more I/O commands and a flag. The flag is set to indicate thatthe location is an indirect address. The location of the one or more I/Ocommands and the flag are extracted from the TCW. The one or more I/Ocommands are gathered based on the location specified by the TCW and theflag, and then the one or more I/O commands are forwarded to the controlunit for execution.

A further exemplary embodiment includes a method for providing indirectdata addressing for a control block at a host computer system configuredfor communication with a control unit. The method includes obtaining aTCW for an I/O operation. The TCW specifies a location of one or moreI/O commands and a flag. The flag is set to indicate that the locationis an indirect address. The location of the one or more I/O commands andthe flag are extracted from the TCW. The one or more I/O commands aregathered based on the location specified by the TCW and the flag. Theone or more I/O commands are then forwarded to the control unit forexecution.

Other articles of manufacture, apparatuses, and/or methods according toembodiments will be or become apparent to one with skill in the art uponreview of the following drawings and detailed description. It isintended that all such additional articles of manufacture, apparatuses,and/or methods be included within this description, be within the scopeof the present invention, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other objects, features, andadvantages of the invention are apparent from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 depicts one embodiment of an I/O processing system incorporatingand using one or more aspects of the present invention;

FIG. 2A depicts one example of a prior art channel command word;

FIG. 2B depicts one example of a prior art channel command word channelprogram;

FIG. 3 depicts one embodiment of a prior art link protocol used incommunicating between a channel and control unit to execute the channelcommand word channel program of FIG. 2B;

FIG. 4 depicts one embodiment of a transport control word (TCW) channelprogram, in accordance with an aspect of the present invention;

FIG. 5 depicts one embodiment of a link protocol used to communicatebetween a channel and control unit to execute the TCW channel program ofFIG. 4, in accordance with an aspect of the present invention;

FIG. 6 depicts one embodiment of a prior art link protocol used tocommunicate between a channel and control unit in order to execute fourread commands of a channel command word channel program;

FIG. 7 depicts one embodiment of a link protocol used to communicatebetween a channel and control unit to process the four read commands ofa TCW channel program, in accordance with an aspect of the presentinvention;

FIG. 8 depicts one embodiment of a control unit and a channel subsystem,in accordance with an aspect of the present invention;

FIG. 9 depicts one embodiment of a TCW in accordance with an aspect ofthe present invention;

FIG. 10 depicts one embodiment of a TCCB in accordance with an aspect ofthe present invention;

FIG. 11 depicts one embodiment of a TCW channel program, in accordancewith an aspect of the present invention;

FIG. 12 depicts one embodiment of a process for providing indirect dataaddressing for a control block; and

FIG. 13 depicts one embodiment of an article of manufactureincorporating one or more aspects of the present invention.

The detailed description explains the preferred embodiments of theinvention, together with advantages and features, by way of example withreference to the drawings.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with an aspect of the present invention, input/output(I/O) is facilitated by allowing a plurality of commands making up asingle I/O operation to be stored in non-contiguous storage. Dependingon factors such as the number of commands and the amount of associatedcontrol data, the length of the required storage may vary from one I/Ooperation to another I/O operation. An exemplary embodiment of thepresent invention utilizes a list of indirect addresses to gathercommand data to be sent to a control unit as part of a single I/Ooperation. This facilitates I/O processing by reducing communicationsbetween components of an I/O processing system used to perform the I/Oprocessing. For instance, the number of exchanges and sequences betweenan I/O communications adapter, such as a channel, and a control unit isreduced. This is accomplished by sending a plurality of commands fromthe I/O communications adapter to the control unit as a single entityfor execution by the control unit.

The plurality of commands (e.g., device command words or “DCWs”) areincluded in a block, referred to herein as a transport command controlblock (TCCB), an address (indirect or direct) of which is specified in atransport control word (TCW). In an exemplary embodiment, the TCW issent from an operating system (OS) or other application to the I/Ocommunications adapter, which in turn forwards the TCCB in a commandmessage to the control unit for processing. The control unit processeseach of the commands absent a tracking of status relative to thoseindividual commands by the I/O communications adapter. The plurality ofcommands is also referred to as a channel program, which is parsed andexecuted on the control unit rather than the I/O communications adapter.

One example of an I/O processing system incorporating and using one ormore aspects of the present invention is described with reference toFIG. 1. I/O processing system 100 includes a host system 101, whichfurther includes for instance, a main memory 102, one or more centralprocessing units (CPUs) 104, a storage control element 106, and achannel subsystem 108. The host system 101 may be a large scalecomputing system, such as a mainframe or server. The I/O processingsystem 100 also includes one or more control units 110 and one or moreI/O devices 112, each of which is described below.

Main memory 102 stores data and programs, which can be input from I/Odevices 112. For example, the main memory 102 may include one or moreoperating systems (OSs) 103 that are executed by one or more of the CPUs104. For example, one CPU 104 can execute a Linux® operating system 103and a z/OS® operating system 103 as different virtual machine instances.The main memory 102 is directly addressable and provides for high-speedprocessing of data by the CPUs 104 and the channel subsystem 108.

CPU 104 is the controlling center of the I/O processing system 100. Itcontains sequencing and processing facilities for instruction execution,interruption action, timing functions, initial program loading, andother machine-related functions. CPU 104 is coupled to the storagecontrol element 106 via a connection 114, such as a bidirectional orunidirectional bus.

Storage control element 106 is coupled to the main memory 102 via aconnection 116, such as a bus; to CPUs 104 via connection 114; and tochannel subsystem 108 via a connection 118. Storage control element 106controls, for example, queuing and execution of requests made by one ormore of the CPU 104 and the channel subsystem 108.

In an exemplary embodiment, channel subsystem 108 provides acommunication interface between host system 101 and control units 110.Channel subsystem 108 is coupled to storage control element 106, asdescribed above, and to each of the control units 110 via a connection120, such as a serial link. Connection 120 may be implemented in anymanner known in the art, including an optical link, employingsingle-mode or multi-mode waveguides in a Fibre Channel fabric (e.g., afibre channel network). Channel subsystem 108 directs the flow ofinformation between I/O devices 112 and main memory 102. It relieves theCPUs 104 of the task of communicating directly with the I/O devices 112and permits data processing to proceed concurrently with I/O processing.The channel subsystem 108 uses one or more channel paths 122 as thecommunication links in managing the flow of information to or from I/Odevices 112. As a part of the I/O processing, channel subsystem 108 alsoperforms the path-management functions of testing for channel pathavailability, selecting an available channel path 122 and initiatingexecution of the operation with the I/O devices 112.

Each channel path 122 includes a channel 124 (channels 124 are locatedwithin the channel subsystem 108, in one example, as shown in FIG. 1),one or more control units 110 and one or more connections 120. Inanother example, it is also possible to have one or more dynamicswitches (not depicted) as part of the channel path 122. A dynamicswitch may be coupled to a channel 124 and a control unit 110 andprovides the capability of physically interconnecting any two links thatare attached to the switch. In another example, it is also possible tohave multiple systems, and therefore multiple channel subsystems (notdepicted) attached to one or more of the control units 110.

Also located within channel subsystem 108 are subchannels (not shown).One subchannel is provided for and dedicated to each I/O device 112accessible to a program through the channel subsystem 108. A subchannel(e.g., a data structure, such as a table) provides the logicalappearance of a device to the program. Each subchannel providesinformation concerning the associated I/O device 112 and its attachmentto channel subsystem 108. The subchannel also provides informationconcerning I/O operations and other functions involving the associatedI/O device 112. The subchannel is the means by which channel subsystem108 provides information about associated I/O devices 112 to CPUs 104,which obtain this information by executing I/O instructions.

Channel subsystem 108 is coupled to one or more control units 110. Eachcontrol unit 110 provides logic to operate and control one or more I/Odevices 112 and adapts, through the use of common facilities, thecharacteristics of each I/O device 112 to the link interface provided bythe channel 124. The common facilities provide for the execution of I/Ooperations, indications concerning the status of the I/O device 112 andcontrol unit 110, control of the timing of data transfers over thechannel path 122 and certain levels of I/O device 112 control.

Each control unit 110 is attached via a connection 126 (e.g., a bus) toone or more I/O devices 112. I/O devices 112 receive information orstore information in main memory 102 and/or other memory. Examples ofI/O devices 112 include card readers and punches, magnetic tape units,direct access storage devices, displays, keyboards, printers, pointingdevices, teleprocessing devices, communication controllers and sensorbased equipment, to name a few.

One or more of the above components of the I/O processing system 100 arefurther described in “IBM® z/Architecture Principles of Operation,”Publication No. SA22-7832-05, 6th Edition, April 2007; U.S. Pat. No.5,461,721 entitled “System For Transferring Data Between I/O Devices AndMain Or Expanded Storage Under Dynamic Control Of Independent IndirectAddress Words (IDAWS),” Cormier et al., issued Oct. 24, 1995; and U.S.Pat. No. 5,526,484 entitled “Method And System For Pipelining TheProcessing Of Channel Command Words,” Casper et al., issued Jun. 11,1996, each of which is hereby incorporated herein by reference in itsentirety. IBM is a registered trademark of International BusinessMachines Corporation, Armonk, N.Y., USA. Other names used herein may beregistered trademarks, trademarks or product names of InternationalBusiness Machines Corporation or other companies.

In one embodiment, to transfer data between I/O devices 112 and memory102, channel command words (CCWs) are used. A CCW specifies the commandto be executed, and includes other fields to control processing. Oneexample of a CCW is described with reference to FIG. 2A. A CCW 200includes, for example, a command code 202 specifying the command to beexecuted (e.g., read, read backward, control, sense and write); aplurality of flags 204 used to control the I/O operation; for commandsthat specify the transfer of data, a count field 206 that specifies thenumber of bytes in the storage area designated by the CCW 200 to betransferred; and a data address 208 that points to a location in mainmemory that includes the data, when direct addressing is employed, or toa list (e.g., contiguous list) of modified indirect data address words(MIDAWs) to be processed, when modified indirect data addressing isemployed. Modified indirect addressing is further described in U.S.application Ser. No. 11/464,613, entitled “Flexibly Controlling TheTransfer Of Data Between Input/Output Devices And Memory,” Brice et al.,filed Aug. 15, 2006, which is hereby incorporated herein by reference inits entirety.

One or more CCWs arranged for sequential execution form a channelprogram, also referred to herein as a CCW channel program. The CCWchannel program is set up by, for example, an operating system, or othersoftware. The software sets up the CCWs and obtains the addresses ofmemory assigned to the channel program. An example of a CCW channelprogram is described with reference to FIG. 2B. A CCW channel program210 includes, for instance, a define extent CCW 212 that has a pointer214 to a location in memory of define extent data 216 to be used withthe define extent command. In this example, a transfer in channel (TIC)218 follows the define extent command that refers the channel program toanother area in memory (e.g., an application area) that includes one ormore other CCWs, such as a locate record 217 that has a pointer 219 tolocate record data 220, and one or more read CCWs 221. Each read CCW 221has a pointer 222 to a data area 224. The data area includes an addressto directly access the data or a list of data address words (e.g.,MIDAWs or IDAWs) to indirectly access the data. Further, CCW channelprogram 210 includes a predetermined area in the channel subsystemdefined by the device address called the subchannel for status 226resulting from execution of the CCW channel program.

The processing of a CCW channel program is described with reference toFIG. 3, as well as with reference to FIG. 2B. In particular, FIG. 3shows an example of the various exchanges and sequences that occurbetween a channel and a control unit when a CCW channel program isexecuting. The link protocol used for the communications is FICON (FibreConnectivity), in this example. Information regarding FICON is describedin “Fibre Channel Single Byte Command Code Sets-3 Mapping Protocol”(FC-SB-3), T11/Project 1357-D/Rev. 1.6, INCITS (March 2003), which ishereby incorporated herein by reference in its entirety.

Referring to FIG. 3, a channel 300 opens an exchange with a control unit302 and sends a define extent command and data associated therewith 304to control unit 302. The command is fetched from define extent CCW 212(FIG. 2B) and the data is obtained from define extent data area 216. Thechannel 300 uses TIC 218 to locate the locate record CCW and the readCCW. It fetches the locate record command 305 (FIG. 3) from the locaterecord CCW 217 (FIG. 2B) and obtains the data from locate record data220. The read command 306 (FIG. 3) is fetched from read CCW 221 (FIG.2B). Each is sent to the control unit 302.

The control unit 302 opens an exchange 308 with the channel 300, inresponse to the open exchange of the channel 300. This can occur beforeor after locate command 305 and/or read command 306. Along with the openexchange, a response (CMR) is forwarded to the channel 300. The CMRprovides an indication to the channel 300 that the control unit 302 isactive and operating.

The control unit 302 sends the requested data 310 to the channel 300.Additionally, the control unit 302 provides the status to the channel300 and closes the exchange 312. In response thereto, the channel 300stores the data, examines the status and closes the exchange 314, whichindicates to the control unit 302 that the status has been received.

The processing of the above CCW channel program to read 4 k of datarequires two exchanges to be opened and closed and seven sequences. Thetotal number of exchanges and sequences between the channel and controlunit is reduced through collapsing multiple commands of the channelprogram into a TCCB. The channel, e.g., channel 124 of FIG. 1, uses aTCW to identify the location of the TCCB, as well as locations foraccessing and storing status and data associated with executing thechannel program. The TCW is interpreted by the channel 124 and is notsent or seen by the control unit 110.

One example of a channel program to read 4 k of data, as in FIG. 2B, butincludes a TCCB, instead of separate individual CCWs, is described withreference to FIG. 4. As shown, a channel program 400, referred to hereinas a TCW channel program, includes a TCW 402 specifying a location inmemory of a TCCB 404, as well as a location in memory of a data area 406or a TIDAL 410 (i.e., a list of transport mode indirect data addresswords (TIDAWs), similar to MIDAWs) that points to data area 406, and astatus area 408.

The processing of a TCW channel program is described with reference toFIG. 5. The link protocol used for these communications is, forinstance, Fibre Channel Protocol (FCP). In particular, three phases ofthe FCP link protocol are used, allowing host bus adapters to be usedthat support FCP to perform data transfers controlled by CCWs. FCP andits phases are described further in “Information Technology—FibreChannel Protocol for SCSI, Third Version (FCP-3),” T10 Project 1560-D,Revision 4, Sep. 13, 2005, which is hereby incorporated herein byreference in its entirety.

Referring to FIG. 5, a channel 500 opens an exchange with a control unit502 and sends TCCB 504 to the control unit 502. In one example, the TCCB504 and sequence initiative are transferred to the control unit 502 in aFCP command, referred to as FCP_CMND information unit (IU) or atransport command IU. The control unit 502 executes the multiplecommands of the TCCB 504 (e.g., define extent command, locate recordcommand, read command as device control words (DCWs)) and forwards data506 to the channel 500 via, for instance, a FCP_Data IU. It alsoprovides status and closes the exchange 508. As one example, finalstatus is sent in a FCP status frame that has a bit active in, forinstance, byte 10 or 11 of the payload of a FCP_RSP IU, also referred toas a transport response IU. The FCP_RSP_IU payload may be used totransport FICON ending status along with additional status information.

In a further example, to write 4 k of customer data, the channel 500uses the FCP link protocol phases, as follows:

1. Transfer a TCCB in the FCP_CMND IU.

2. Transfer the IU of data, and sequence initiative to the control unit502. (FCP Transfer Ready Disabled)

3. Final status is sent in a FCP status frame that has a bit active in,for instance, byte 10 or 11 of the FCP_RSP IU Payload. The FCP_RES_INFOfield or sense field is used to transport FICON ending status along withadditional status information.

By executing the TCW channel program of FIG. 4, there is only oneexchange opened and closed (see also FIG. 5), instead of two exchangesfor the CCW channel program of FIG. 2B (see also FIG. 3). Further, forthe TCW channel program, there are three communication sequences (seeFIGS. 4-5), as compared to seven sequences for the CCW channel program(see FIGS. 2B-3).

The number of exchanges and sequences remain the same for a TCW channelprogram, even if additional commands are added to the program. Compare,for example, the communications of the CCW channel program of FIG. 6with the communications of the TCW channel program of FIG. 7. In the CCWchannel program of FIG. 6, each of the commands (e.g., define extentcommand 600, locate record command 601, read command 602, read command604, read command 606, locate record command 607 and read command 608)are sent in separate sequences from channel 610 to control unit 612.Further, each 4 k block of data (e.g., data 614-620) is sent in separatesequences from the control unit 612 to the channel 610. This CCW channelprogram requires two exchanges to be opened and closed (e.g., openexchanges 622, 624 and close exchanges 626, 628), and fourteencommunications sequences. This is compared to the three sequences andone exchange for the TCW channel program of FIG. 7, which accomplishesthe same task as the CCW channel program of FIG. 6.

As depicted in FIG. 7, a channel 700 opens an exchange with a controlunit 702 and sends a TCCB 704 to the control unit 702. The TCCB 704includes the define extent command, the two locate record commands, andthe four read commands in DCWs, as described above. In response toreceiving the TCCB 704, the control unit 702 executes the commands andsends, in a single sequence, the 16 k of data 706 to the channel 700.Additionally, the control unit 702 provides status to the channel 700and closes the exchange 708. Thus, the TCW channel program requires muchfewer communications to transfer the same amount of data as the CCWchannel program of FIG. 6.

Turning now to FIG. 8, one embodiment of channel 124 in the channelsubsystem 108 and the control unit 110 of FIG. 1 that support TCWchannel program execution are depicted in greater detail. The controlunit 110 includes CU control logic 802 to parse and process commandmessages containing a TCCB, such as the TCCB 704 of FIG. 7, receivedfrom the channel 124 via the connection 120. The CU control logic 802can extract DCWs and control data from the TCCB received at the controlunit 110 to control a device, for instance, I/O device 112 viaconnection 126. The CU control logic 802 sends device commands and datato the I/O device 112 and receives status information and other feedbackfrom the I/O device 112. For example, the I/O device 112 may be busybecause of a previous reservation request targeting I/O device 112. Tomanage potential device reservation contention issues that can arisewhen the control unit 110 receives multiple requests to access the sameI/O device 112, the CU control logic 802 keeps track of and storesdevice busy messages and associated data in a device busy queue 804.

The control unit 110 may further include other buffer or memory elements(not depicted) to store multiple messages or status informationassociated with communications between the channel 124 and the I/Odevice 112. For example, a register located on the control unit 110 mayinclude a maximum control unit exchange parameter that defines themaximum number of open control unit exchanges that the control unit 110supports.

The channel 124 in the channel subsystem 108 includes elements tosupport communication with the control unit 110. In an exemplaryembodiment, the CHN control logic 806 controls communication between thechannel subsystem 108 and the control unit 110. The CHN control logic806 may directly interface to the CU control logic 802 via theconnection 120 to send commands and receive responses, such as transportcommand and response IUs. Alternatively, messaging interfaces and/orbuffers (not depicted) can be placed between the CHN control logic 806and the CU control logic 802.

An exemplary embodiment of a transport control word (TCW) 900 isdepicted in FIG. 9. The TCW 900 is utilized by the channel 124 to set upthe I/O operation and is not sent to the control unit 110. The TCWdepicted in FIG. 9 provides for indirect addressing of a TCCB byutilizing a TCCB TIDAL flag and a TCCB address.

In an exemplary TCW 900 depicted in FIG. 9, a format field 902 equal to“00b” indicates that what follows is a TCW 900. The TCW 900 alsoincludes reserved bits 904 for possible future use.

The TCW 900 also includes a flags field 906. The first five bits of theflags field 906 are reserved for future use and are set to zero. Thesixth bit of the flags field 906 is a TIDAL read flag. In an exemplaryembodiment, the TIDAL read flag is set (e.g., to one) when theinput-data address field 918 contains an address of a TIDAL. If theTIDAL read flag is reset (e.g., to zero), then the input-data addressfield 918 contains a data address. The seventh bit of the flags field906 is the TCCB TIDAL flag. In an exemplary embodiment, the TCCB TIDALflag is set to one when the TCCB address field 922 contains an addressof a TIDAL. If the TCCB TIDAL flag is set to zero, then the TCCB addressfield 922 directly addresses the TCCB. The TCCB TIDAL flag allows theoperating system software or the hyper-visor to layer function andprefix user channel programs. The eighth bit of the flags field 906 is aTIDAL write flag. In an exemplary embodiment, the TIDAL write flag isset to one when the output-data address field 916 contains an address ofa TIDAL. If the TIDAL write flag is set to zero, then the output-dataaddress field 916 contains a data address.

The ninth through twenty-forth bits of the flags field 906 is reservedfor future use.

The TCW 900 also includes a TCCB length field 910 which indirectlyrepresents the length of the TCCB and may be utilized to determine theactual length of the TCCB.

The read/write bits 912 in the TCW 900 are utilized to indicate whetherdata is being read and/or written as a result of executing the TCW 900.In an exemplary embodiment, the read bit in the read/write 912 bits isset to one to indicate that input data is being transferred from an I/Odevice 112 to system storage (e.g., main memory 102) in the host system101 as a result of executing the TCW 900. The write bit in theread/write bits 912 is set to one to indicate that output data is beingtransferred from system storage (e.g., main memory 102) in the hostsystem 101 to an I/O device as a result of executing the TCW 900.

The output-data address field 916 includes the address for the outputdata (if any). As described previously, the contents of the output-dataaddress field 916 may be an address of a TIDAL for output data or theactual address of the output data. The input-data address field 918includes the address for the input data (if any). As describedpreviously, the contents of the input-data address field 918 may be anaddress of a TIDAL for input data or the actual address of the inputdata. In an exemplary embodiment, the output-data address field 916 andthe input data address field 918 are implemented as sixty-four bitaddresses.

The TCW 900 also includes a transport-status-block address field 920. Aportion (e.g., the extended status part) of a completion status in atransport response IU for an I/O operation is stored at this address.The TCCB address field 922 in the TCW 900 includes an address where theTCCB is located in system storage. As described previously, the TCCB isthe control block where the DCWs to be executed for the TCW 900 reside.Also as described previously, the contents of the TCCB address field 922may be an address of a TIDAL for the TCCB or the actual address of theTCCB. In an exemplary embodiment, the transport-status-block addressfield 920 and the TCCB address field 922 are implemented as sixty-fourbit addresses.

The output count field 924 in the TCW 900 indicates the amount of outputdata to be transferred by the TCW/TCCB for an output operation. In anexemplary embodiment, the output count field 924 specifies the number ofbytes in the output storage area designed by the TCW (the output-dataaddress 916) to be transferred. The input count field 926 in the TCW 900indicates the amount of input data to be transferred by the TCW/TCCB foran input operation. In an exemplary embodiment, the input count field926 specifies the number of bytes in the input storage area designed bythe TCW (the input-data address 918) to be transferred. Severaladditional fields in the TCW 900 are reserved: reserved field 928,reserved field 930 and reserved field 932. The interrogate-TCW addressfield 934 contains the address of another TCW and is used by the channel124 to interrogate that state of an operation under the initiative of acancel sub-channel I/O instruction.

The TCW depicted in FIG. 9 is one example of how a command word can beconfigured. Other configurations are possible where additional fieldsare included and/or fields depicted in FIG. 9 are not included.

FIG. 10 depicts one embodiment of a TCCB 1000 in accordance with anaspect of the present invention. The TCCB 1000 in FIG. 10 is located atthe address indicated in the TCCB address field 922 in the TCW 900. Thisaddress may be a direct address or an indirect address, allowing thecontents of the TCCB 1000 to be in one storage location or to be spreadamong multiple non-contiguous storage locations. As describedpreviously, the TCCB 1000 is a control block built by software and thenthe channel 124 sends it to a control unit 110 (e.g., in a TransportCommand IU) for execution. The TCCB 1000 contains the commands to beexecuted by the control unit 110 and any control data required by thecommands. The channel 124 does not look at the contents of the TCCB1000. The channel 124 packages the TCCB 1000 and sends it to the controlunit 110. This allows FCP transport protocols to be utilized instead ofFICON.

The TCCB 1000 includes a transport control area header (TCAH) 1002which, in an exemplary embodiment, includes information about thetransmit control area (TCA) 1004 and operations within the TCA 1004(e.g., length, service code). In an exemplary embodiment the TCAH 1002includes a format control field for specifying information such as theformat of the TCCB (e.g., variable length CDB format), the modeassociated with the TCCB (e.g., transport mode), service action codesset aside to be used as vendor unique code points, and a field toprovide the control unit the priority in which to execute this TCCB1000.

The TCCB 1000 depicted in FIG. 10 also includes a variable length TCA1004 which includes one or more DCWs 1006 and corresponding DCW controldata 1008, if any for each DCW 1006. The DCW control data 1008 may be ofvariable length. In an exemplary embodiment, each DCW 1006 includes acommand code, flags (chaining), control data length, and read/write datalength. DCW control data 1008 is optional (depending on the DCW 1006)and includes control parameters for its corresponding DCW 1006. Forexample, DCW control data 1008 may include define extent and/or prefixparameters. In an exemplary embodiment, the DCW control data 1008follows its corresponding DCW 1006 within the TCA 1004 and is notpointed to by the DCW 1006.

In addition, the TCCB 1000 includes a TCA trailer (TCAT) 1010 thatcontains data such as the count of the bytes to be transferred in theTCCB 1000 and a check word field to check the integrity of the TCCB1000.

FIG. 11 depicts one embodiment of a TCW channel program 1100, inaccordance with an aspect of the present invention. As shown in FIG. 11,the TCW channel program 1100 includes a TCW 1102 specifying a locationin memory of a TCCB 1104 or TIDAL 1112 (i.e., a list of transportindirect data address words (TIDAWs)) that points to the location forthe TCCB 1104. In addition, the example channel program 1100 depicted inFIG. 11 includes a location in memory of an input data area 1106 or aTIDAL 1110 that points to the input data area 1106, and a status area1108.

FIG. 12 depicts one embodiment of a process for providing indirect dataaddressing for a control block (e.g., a TCCB) in accordance with anaspect of the present invention. In an exemplary embodiment, theprocessing depicted in FIG. 12 occurs at a host computer system that isin network communication with a control unit. The host computer systemmay include an I/O processing system that executes the process.Additionally, the I/O processing system may include channel subsystemthat executes the process. At block 1202, a TCW is obtained by the hostcomputer. In an exemplary embodiment, the TCW is obtained (or received)from an operating system running on the host computer. The TCW includesa TCCB address 922 and a TCCB TIDAL flag located in the flags field 906.At block 1204, the TCCB address 922 and TCCB TIDAL flags are extractedfrom the TCW.

At block 1206, it is determined if the TCCB TIDAL flag is set. If theTCCB TIDAL flag is set, then the TCCB address 922 is an indirect dataaddress and processing continues at block 1210. At block 1210, the TCCBis gathered from the location specified by the TCW. Because the addressis an indirect address, the TCCB address 922 includes an address of aTIDAL. The TIDAL includes a list of addresses that point to a pluralityof storage locations that collectively make up the TCCB. Processing thencontinues at block 1212.

If the TCCB TIDAL flag is not set, as determined at block 1206, then theTCCB address 922 is a direct data address and processing continues atblock 1208. At block 1208, the TCCB is gathered from the locationspecified by the TCW. Because the address is a direct address, the TCCBis located at the address specified by the TCCB address 922. Processingthen continues at block 1212.

At block 1212, the I/O operation, including the TCCB is forwarded to acontrol unit for execution.

Technical effects of exemplary embodiments include the ability to spreadthe TCCB among non-contiguous storage locations. This may lead toperformance improvements due to the ability to easily add on to contentsof the TCCB and due to reduced contention for particular storagelocations. Technical effects also include the ability to have a variablelength TCCB which allows for flexibility in grouping commands togetherfor transmission to a control unit.

As described above, embodiments can be embodied in the form ofcomputer-implemented processes and apparatuses for practicing thoseprocesses. In exemplary embodiments, the invention is embodied incomputer program code executed by one or more network elements.Embodiments include a computer program product 1300 as depicted in FIG.13 on a computer usable medium 1302 with computer program code logic1304 containing instructions embodied in tangible media as an article ofmanufacture. Exemplary articles of manufacture for computer usablemedium 1302 may include floppy diskettes, CD-ROMs, hard drives,universal serial bus (USB) flash drives, or any other computer-readablestorage medium, wherein, when the computer program code logic 1304 isloaded into and executed by a computer, the computer becomes anapparatus for practicing the invention. Embodiments include computerprogram code logic 1304, for example, whether stored in a storagemedium, loaded into and/or executed by a computer, or transmitted oversome transmission medium, such as over electrical wiring or cabling,through fiber optics, or via electromagnetic radiation, wherein, whenthe computer program code logic 1304 is loaded into and executed by acomputer, the computer becomes an apparatus for practicing theinvention. When implemented on a general-purpose microprocessor, thecomputer program code logic 1304 segments configure the microprocessorto create specific logic circuits.

While the invention has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims. Moreover, the use of the terms first, second, etc. do not denoteany order or importance, but rather the terms first, second, etc. areused to distinguish one element from another. Furthermore, the use ofthe terms a, an, etc. do not denote a limitation of quantity, but ratherdenote the presence of at least one of the referenced item.

1. A computer program product for facilitating input/output (I/O)processing for an I/O operation at a host computer system configured forcommunication with a control unit, the computer program productcomprising: a tangible storage medium readable by a processing circuitand storing instructions for execution by the processing circuit forperforming a method comprising: obtaining a transport command word (TCW)for an I/O operation, the TCW specifying a location and a flag;extracting the specified location and the flag from the TCW; obtaining amessage from the specified location responsive to the flag having afirst value, the message comprising one or more I/O commands; gatheringone or more I/O commands from command locations specified by a list ofaddresses to form the message responsive to the flag having a secondvalue, the message comprising the gathered one or more I/O commands; andforwarding the message to the control unit for execution.
 2. Thecomputer program product of claim 1 wherein the list of addressescomprises two or more I/O commands, and the forwarded message comprisesthe two or more I/O commands.
 3. The computer program product of claim 1wherein the one or more I/O commands are included in a transport commandcontrol block (TCCB) and the location specified by the TCW is thelocation of the TCCB.
 4. The computer program product of claim 3 whereinthe TCCB further includes a header and a variable length transportcontrol area, the header comprising information about the variablelength transport control area, the variable length transport controlarea comprising one or more I/O commands, the header configured tospecify a format of at least one of the one or more I/O commands and thegathered one or more I/O commands.
 5. The computer program product ofclaim 3 wherein the TCCB further includes a trailer for providing acheck word and specifying the amount of data to transfer.
 6. Thecomputer program product of claim 1 wherein at least one of the one ormore I/O commands and the gathered one or more I/O commands includescommand codes and control data.
 7. The computer program product of claim1 wherein the host computer system includes a channel subsystem and themethod is performed by the channel subsystem.
 8. The computer programproduct of claim 1 wherein the TCW is obtained from a host operatingsystem.
 9. An apparatus for providing indirect data addressing for acontrol block at a host computer system configured for communicationwith a control unit, the host computer system performing: obtaining aTCW for an I/O operation, the TCW specifying a location and a flag;extracting the specified location and the flag from the TCW; obtaining amessage from the specified location responsive to the flag having afirst value, the message comprising one or more I/O commands; gatheringone or more I/O commands from command locations specified by a list ofaddresses to form the message responsive to the flag having a secondvalue, the message comprising the gathered one or more I/O commands; andforwarding the message to the control unit for execution.
 10. Theapparatus of claim 9 wherein the list of addresses comprises two or moreI/O commands, and the forwarded message comprises the two or more I/Ocommands.
 11. The apparatus of claim 9 wherein the one or more I/Ocommands are included in a transport command control block (TCCB) andthe location specified by the TCW is the location of the TCCB.
 12. Theapparatus of claim 11 wherein the TCCB further includes a header and avariable length transport control area, the header comprisinginformation about the variable length transport control area, thevariable length transport control area comprising one or more I/Ocommands, the header configured to specify a format of the one or moreI/O commands.
 13. The apparatus of claim 11 wherein the TCCB furtherincludes a trailer for providing a check word and specifying the amountof data to transfer.
 14. The apparatus of claim 9 wherein at least oneof the one or more I/O commands and the gathered one or more I/Ocommands includes command codes and control data.
 15. A method forproviding indirect data addressing for a control block at a hostcomputer system configured for communication with a control unit, themethod comprising: obtaining a TCW for an I/O operation, the TCWspecifying a location and a flag; extracting the specified location andthe flag from the TCW; obtaining a message from the specified locationresponsive to the flag having a first value, the message comprising oneor more I/O commands; gathering one or more I/O commands from commandlocations specified by a list of addresses to form the messageresponsive to the flag having a second value, the message comprising thegathered one or more I/O commands; and forwarding the message to thecontrol unit for execution.
 16. The method of claim 15 wherein the oneor more I/O commands are included in a transport command control block(TCCB) and the location specified by the TCW is the location of theTCCB.
 17. The method of claim 16 wherein the TCCB further includes atrailer to provide a check word and specifying the amount of data totransfer.
 18. The method of claim 15 wherein at least one of the one ormore I/O commands and the gathered one or more I/O commands includescommand codes and control data.
 19. The method of claim 15 wherein thehost computer includes a channel subsystem and the method is performedby the channel subsystem.
 20. The method of claim 15 wherein the TCW isobtained from a host operating system.